![]() ![]() I no longer own anything with DOT5 in it, though I have owned several. My former brake parts supplier in Farmingdale Long island told me he was putting his kids through college thanks to his contract with the US Postal System to repair their truck brake systems, because they were using DOT5. There is supposed to be a change and flush schedule. But what this Wagner engineer pointed out was that the DOT 5 sellers haven't been telling people is that the government does not leave DOT 5 and forget about it. Yes, the DOT 5 sellers have used that "the government uses it" line since they first started selling it. ![]() However, it has it's limits and rarely does anyone stay within those limits by flushing a new quart of DOT 3 through every two-three years in humid climates, as the manufactures recommend, or 5-6 years in dryer climates.īack 25 years ago, that Wagner engineer told me to watch for the new DOT 4 fluids coming from Europe because they have a much better anticorrosion package. Dot 3 is designed to work with water and protect the system. Only after what the Wagner engineer call, "gross contamination". The US Government has been using it for decades for exactly that reason. If you take apart a DOT5 system often (not always) there is no rust damage at all. DOT5 does not chemically attract water like DOT3 does, and in old open-to-atmosphere systems the water problem is far less severe than it is with DOT3 because far less gets in. The damage, and the worst fluid, is always at the bottom of the cylinder. Nobody has time for that trackside.īut that is almost exactly what happens with DOT3. The reason you don't see DOT5 much in racing is that it is such a pain in the ass to bleed. If your going to use DOT5 in your car don't assume it's good for life. Thinking that you never have to inspect inside the brake system, or flush with new DOT 5 every few years, may shorten your life. And it not only causes rust, that water can freeze in winter. Any frozen water being pushed around in cylinders might cause brake system problems. If it boils into steam it greatly expands. That can lead to boiling in heavy braking because unlike DOT 3 & 4 the water isn't mixed with the DOT5 so it's boiling point is very low. With DOT 5 it can't deal with that water vapor so the water collects in the lowest points. The molecule's can penetrate right though the hose walls because of vapor pressure being higher on the outside in humid weather. He said that Wagner did tests with brake hoses and found they can't seal out water molecules, which are some of the smallest in nature. I had a nice chat with a Wagner Lockheed engineer about 25 years ago about brake fluids. I've had to open and inspect the DOT5 filled systems of several customers late 20s and early 30s cars over the years and every one of them showed signs of water pooling and rust in the lowest parts of the system - such as the bottom of the master cylinder and the wheel cylinders.Īnd that's not the only way water gets in. As the brake pedal moves fluid in and out of the master cylinder and reservoir, outside air is pumped in/out also. Moisture gets into many old brake systems because the reservoirs do not have a rubber sealed cap like modern cars. The OEM car manufacturers still use ester alcohol in new cars with anti-lock brakes and tell you to flush and replace it every few years to protect expensive anti-lock pumps. ![]() I used silicone fluid in trailers equipped with surge brakes and a couple of antique motorcycles because they sat and never really had a problem but it is an interesting and controversial theory. A lot of race teams refuse to use it because if that water gets gathers in or near brake cylinders or calipers it can boil on hard braking and create steam which then causes brake failure at the time they are needed the most. If water gets into the system from any source it remains as concentrated water because the silicone cant absorb or mix with it. Silicone is inaqueous, won't mix with water. We all know the alcohol in Dot 3 does absorb moisture over time but the alcohol readily mixes with both the water and the ester oil so there is no concentration of water and if you replace it ever 3yrs or so it won't absorb enough to rust. I understand very much why you would want to change from Dot 3 ester alcohol to Dot 5 Silicone fluid, it wont rust, right? Well from what I have read that's a definite maybe.
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